The invention relates to a method and an arrangement for monitoring the operation of a gas flow control element including a swirl flap in an internal combustion engine.
In multi-cylinder internal combustion engines having fuel direct injection, an optimized mixture formation or mixture distribution in the combustion chamber is sought for an optimized combustion in the combustion chambers of the individual cylinders. A decisive contribution for this purpose can be made by a suitably directed air flow into the combustion chambers. The nature and course of the air flow are significantly influenced during induction by the intake channels and the nature of the inflow of the air into the cylinders. The optimal type and the intensity of the directed air movement in the cylinder is dependent upon various factors and deviations from the optimum can lead to various problems. An air movement which is too low can, for example, lead to the following: a poor utilization of the air, an incomplete combustion or to combustion misfires. Increasing emissions of smoke can occur when the swirling of air is too intense, for example, in diesel engines. This is so because, for the same injection duration, the fuel is injected into already combusted air regions.
Since the intake channels have a defined geometry, similar air flow conditions result in conventional induction systems over the entire rpm range and for various load conditions. To optimize the air flow, and therefore to optimize the combustion, so-called swirl flaps are utilized as gas flow control elements in the intake system upstream of the cylinders. These swirl flaps are drivable movable control elements which influence the nature and intensity of the air flow into the combustion chamber and especially lead to swirling or swirl formations. The air flow can be optimized by the operating-point dependent control of swirl flaps, for example, via a stepper motor. The swirl flap position can, for example, be stored in a characteristic field of the motor control as a function of the engine rpm and of the engine load or of the charge.
For defects in the area of swirl flaps or of their control, these swirl flaps cannot optimally satisfy the provided function so that operating disturbances can occur which can be attributed to the non-optimized air flow into the cylinders. For example, and as mentioned, this can lead to incomplete combustions or combustion misfires which lead to a deterioration of the exhaust gas. The detection of defects in the region of swirl flaps and/or of their drive is therefore desirable.
Gas flow control elements can be provided also in the exhaust system of the engine, that is, downstream of the cylinders. With such control elements, the exhaust-gas counterpressure can be influenced which works back upon the combustion processes in the cylinders. These control elements are mostly referred to as exhaust-gas flaps.
It is an object of the invention to provide a cost-effectively realizable method for monitoring the operation of gas flow control elements and especially of swirl flaps in internal combustion engines. The implementation of the method in internal combustion engines, wherein the control includes units for monitoring and, if required, influencing the smooth running of the engine, can be realized without additional sensors or other hardware components.
According to a feature of the invention, a detection of the rough running of the engine is carried out while forming at least one rough-running signal representing the rough running of the engine. For checking the operability, a change of the position of the gas flow control element is attempted and/or effected by, if required, driving the gas flow control element for a short time. A detection of the rough-running signal as a function of the drive of the gas flow control element takes place, that is, as a function of the change of the position of the gas flow control element or as a function of an attempt to change the position of the gas flow control element. The rough-running signal is thus viewed especially at or near the time of driving the gas flow control element. Here, it can be especially so that no significant rough running change results, notwithstanding driving the gas flow control element. Depending upon whether, and in which way, the rough running signal changes after driving the gas flow control element, a conclusion can be drawn as to the operability of the gas flow control element, that is, whether it is driven or if there are disturbances in this region.
In view of the foregoing, the invention provides for drawing a conclusion as to the operability of the gas flow control element by monitoring the engine rough running in the context of driving a gas flow control element. This driving of the gas flow control element is carried out preferably exclusively for test purposes with the objective of a position change. Here, and, for example, in the case of a swirl flap, one proceeds from the consideration that a deteriorated combustion, as it can occur because of a defective swirl flap, leads, as a rule, also to an increase of the rough running of the engine. If now the time-dependent trace of the rough running of the engine is viewed especially in the context of the time point of the control of the swirl flap, then specific rough running changes or the absence of expected changes of the rough running are evaluated as an indication as to an intact operation of the swirl flap control or as an indication of a defect in the actuation of the swirl flap.
The same considerations apply to exhaust-gas flaps.
The term xe2x80x9crough runningxe2x80x9d in the context of this disclosure relates to changes in angular acceleration of the crankshaft which can occur because of the combustion processes in the individual cylinders of the engine. Accordingly, the rough running is based on torque scatterings between the cylinders of the engine. This rough running can be determined, for example, by an evaluation of the rpm fluctuations at the crankshaft (or at the camshaft).
To realize the invention, any suitable method for observing the rough running of the engine can be used. Preferred methods, which form an index for the engine rough running by evaluating rpm fluctuations, are disclosed in German patent publication 4,001,333; and U.S. Pat. Nos. 5,359,518 and 5,231,869 as well as U.S. patent application Ser. No. 07/818,884, filed Jan. 10, 1992, now abandoned (corresponds to German patent publication 4,138,765) which are incorporated herein by reference. Especially so-called segment times can be detected for evaluating the time-dependent trace of the rotational movement of the crankshaft or the camshaft. This will be explained hereinafter in connection with an embodiment.
It is known to form rough-running values (especially also by viewing segment times), inter alia, for the detection of combustion misfires as disclosed in U.S. Pat. No. 5,861,553 incorporated herein by reference. It is noted that rough-running values are also formed in systems for equalizing cylinders wherein especially the equalization or adaptation of torque contributions individual to cylinders is understood as disclosed, for example, in German patent publication 198 28 279 which is incorporated herein by reference especially with respect to the formation of rough-running values.
The term xe2x80x9cgas flow control elementxe2x80x9d is understood to mean in the context of this disclosure each suitable control element with which the air flow into the combustion chamber of a cylinder or the flow relationships and pressure relationship downstream of the cylinder can be influenced. Control elements of this kind do not necessarily have to be tiltable or pivotable but can, for example, also be configured as slides or the like.
In an especially simply realizable embodiment, the monitoring of the operation of the gas flow control element (especially of the swirl flap) can be carried out with the aid of a difference formation between suitably formed rough-running signals. In this way, an especially rapid reacting monitoring operation is possible. Especially, at first a quasi steady-state operation of the engine can be awaited and, in this quasi steady-state operation, the rough running of the engine is detected and is utilized for the formation of a first rough-running signal. Close in time or immediately thereafter, a driving of the gas flow control element takes place with the object of changing the position of the control element. Thereafter, and by detecting the engine rough running, a second rough-running signal is formed. A rough-running difference signal is formed from the difference between the first and second rough-running signals. The amount of this difference is compared to a pregiven threshold value.
If, for example, in the case of the swirl flap diagnosis, the rough-running difference signal lies above the threshold value, then one can assume an operationally sound swirl flap because the swirl flap position has changed apparently because of the control of the swirl flap. This leads to air flow changes and therefore temporarily to an increase of rough running. If such a significant increase in rough running is determined, then a positive function signal is outputted which represents the operability of the swirl flap control.
If, in contrast, a drop below the threshold value is determined, this is evaluated as an indication of a disturbance of the function because the drive did not lead to an intended position change of the swirl flap and therefore to a temporary increase in the rough running. In the case of a suspected defect, a negative signal can be generated which represents the disturbance of function. This disturbance signal can be utilized to initiate at least one renewed control check and/or to initiate measures to remove the function disturbance.
For diagnosis, the first and the second rough-running signal can be used also in another manner and, if required, without a difference formation, for example, with the aid of other suitable mathematical functions, for forming a combination signal from which the function signal can be derived.
In another embodiment of the invention, and after driving the gas flow control element (especially the swirl flap), first an ignition angle change is effected in dependence upon the position change of the gas flow control element, before the evaluation of the rough running is continued, for example, by detecting the second rough-running signal. This variation is advantageous in spark-ignition engines and considers that, for example, a retarded ignition can occur, under circumstances, for example, because of an increase of the swirl movement of the air flow. This is compensated by the mentioned ignition angle change so that an increase of the engine rough running, which is perhaps observed after a change of the throttle flap position, cannot be attributed originally to an unfavorable ignition angle position.